1. Field of the Invention
The present invention relates to novel stabilized visual indicating paste compositions and to the utilization of the same to detect the presence, and particularly the level, of aqueous solutions when admixed with hydrocarbons, such as gasoline, oil or other fuel and petroleum fractions. More particularly, the present invention is concerned with stabilized visual indicating paste compositions which are capable of undergoing a change in color upon contact with aqueous solutions which may be present in minor amounts, generally as a separate phase, in hydrocarbon storage tanks, delivery vehicles, distribution systems, and the like. The compositions of the invention are particularly adapted for use in determining the water level in the bottom of gasoline storage and transportation tanks to determine the amount of water resting in the tank partially filled with the hydrocarbon, and when the water contains oxygenated blending components, such as ethers and alcohols.
2. Description of the Prior Art
Paste compositions detecting the level or presence of water have been disclosed in the prior art. In U.S. Pat. No. 2,520,993, there is disclosed a composition illustrative of such pastes comprising a water soluble cobalt thiocyanate and a finely dispersed filler material having a color other than that of the thiocyanate. Polish Pat. No. 94,388 discloses a paste, which changes color from blue to white or light pink upon contact with water, obtained by blending ammonium thiocyanate with cobalt chloride, an aromatic amine, glycerol, paraffinic oil and ground chalk. Austrian Patent 360,961 discloses a self-adhesive indicator paste useful for detecting pH, nitrate and iron, coated on a polystyrene carrier, which is prepared by impregnating the carrier material with one or more indicator solutions containing Ethyl Red, bromxylenol blue, and acetone.
Pastes for detecting the level of water in hydrocarbon storage tanks, such as gasoline tanks employed at service stations, have been commercially available. In use, such pastes undergo a color change after contacting with water. However, certain of these commercially available pastes are deficient in one or more characteristics, for example, in failing to exhibit a sharp and distinct color change, or alternatively, in having high solubility in the water or hydrocarbon phases, or comparatively short shelf life, or in exhibiting high hygroscopicity. A particular difficulty has been encountered with conventional water indicating pastes when attempts have been made to obtain accurate readings of the water level in tanks and delivery systems for hydrocarbons, such as gasoline, wherein the water contains oxygenated gasoline blending components leached from the gasoline, which components preclude the obtainment of a sharp and distinct color change or cause bleed or run off the measuring probe coated with the paste when contacted with such oxygen-containing aqueous solutions.
In U.S. application Ser. Pat. No. 490,744 filed May 2, 1983, of F. W. Melpolder and J. G. Victor entitled "Composition and Probe for Detection of Water," there is disclosed a visual indicating paste composition for producing a detectable color change upon contact with an aqueous solution comprising a water soluble indicator dye capable of changing color in the pH range between about 7 and 11 and an insoluble, inorganic base in the form of a caustic powder dispersed in a liquid carrier capable of absorbing water but which is not rapidly leached by water or hydrocarbon. It has been found, however, that the water indicating paste disclosed in said application, may turn color during storage due to the introduction of trace quantities of water originating from one or more sources. Hence, water may penetrate the paste should humid conditions exist during manufacture or storage of the paste or water may be absorbed by the paste while opening the container during each application of the paste by the user. In addition, water may be introduced with the ingrediants, such as liquid carriers, employed in formulation of the paste.